I overlooked the fact that passing an imported module object to $DONE will
correctly fail the test.
I still think this way of writing the test is unclear, though.
This proposes a `harness/asyncHelpers.js` file with two helpers in it,
`asyncTest()` and `assert.throwsAsync()`. See the RFC for further
motivation and details.
Note the draft RFC process in https://github.com/tc39/test262/pull/3525.
My idea for this pull request is that besides being an RFC in its own
right, we use it as a test case for the process. That is, we follow the
draft RFC process and hopefully either validate it, or surface changes
that need to be made, after which we can land the RFC process in our
documentation.